You will need at least ten people for this activity. Assign each child a planet (or the sun) and give them big name cards or cut outs of their planet with the name written on the back. Draw rings on concrete with sidewalk chalk. Arrange the children according to their place in the solar system. Tell each planet which direction they orbit in, whether they spin fast or slow and any other characteristic they can act out. Let the children "orbit" the sun and reenact the solar system. If there are more than nine kids, either make multiple groups or have some of the children be stars or moons.
This is a commonly-used project to learn about the solar system because it is effective. There are kits available for purchase from most craft stores and online, but you can also put it together from scratch. Buy 10 styrofoam balls in sizes that are relative to one another for the sun and each of the planets. Paint the sun and each of the balls according to which planet they represent. Use wooden sticks or wire to attach the planets to the sun.
Take a shoebox. On one of the shorter sides of the outside of the box, draw out the solar system from a bird's eye view so that all the planets can be viewed at once. Cut out the shapes of the planets and sun. Create stars by poking a push pin around the planets. You can also create the orbit paths by drawing them in with the push pin. On the opposite side of the box, cut out a small viewing hole in the center. Make sure the lid of the box is on. Look through the viewing hole and point it toward the sky. An illuminated solar system will be visible.
Use round foods such as cherries, grapes, peas, meatballs, oranges, blueberries or donut holes. Place them in position as the solar system. Each child can have their own solar system and eat it for a snack as well!